I have a 2-stage variable-speed Goodman high efficiency furnace. There is an 'O' (reversing valve) terminal on the terminal block with the other thermostat connections. None of the sample wiring diagrams show it being used.
I am trying to figure out what purpose this (an O terminal) serves on a furnace. The only thing I could come up with is maybe O on and G off tells the furnace that in a heat pump setup the heat pump is operating in heat mode, so the furnace fan should switch to heat speed instead of cooling speed? But that doesn't really make sense either since if it wasn't a heat pump there would be no O connection.
Which raises the question, when used with a heat pump, can the furnace tell when the heat pump is operating in heat mode and switch the fan to heat speed?
(I did find a wiring diagram for a Goodman fossil fuel kit (which I don't have, I have an IAQ stat with built-in fossil fuel capability)), and it shows O on the furnace wired to O on the 'furnace' section of the fossil fuel board, and that in turn connects to O on the heat pump and O on the stat.
"I gots ta know"